Variable focus mirrors which have been proposed in the prior art have generally relied on uniform loading of a plate, as by a vacuum over the entire rear surface, to produce a cup shaped mirror. The shape thus obtained for a uniform thickness plate is neither parabolic nor spherical and, in an effort to produce the desired shape the plate thickness is made non-uniform. A modification thereof applies a non-uniform load to a plate by a plurality of unevenly loaded mechanical connections attached to the rear of the plate. Another method of variably flexing a disk, wherein the circumferential edge of the disk is placed in a circular frame of adjustable diameter, has also been described in the prior art.
The present invention is a departure from prior art in that the disk is flexed by application of a force uniformly distributed along the outer edge, urging the disk against a concentric fixed annular fulcrum and causing the portion of disk inside the smaller ring to flex into a substantially spherical shape. Alternately, the inner ring can move the disk against a fixed annular fulcrum at the rim, obtaining similar results. The degree of flexure establishes the focal length of the mirror which is readily adjusted by the controlled force applied to the disk. The curvature of the mirror may be either concave or convex according to the direction of the applied moment with respect to the mirrored surface of the disk. The deflected shape remains spherical for all ranges of focal length, as long as the disk remains elastic.
The present invention is particularly useful in laser application where the rugged nature of the device will assure longevity even when high energy laser beams are reflected.
In one embodiment of the present invention, the flat surface disk of uniform cross section is supported by the rim in a hollowed out piston. A frame structure surrounds the piston and is provided with an annular ring contacting the face of the disk. Relative displacement of the piston and frame applies a force to the disk which flexes into a spherical surface. The driving force on the piston is preferably applied hydraulically although any suitable driving means may be employed. It is an object of this invention to provide a controllable variable focus mirror for laser application.
It is another object of this invention to provide a spherical surface over a large range of focal length with means for adjusting the radius of curvature of the surface.
It is a further object to promote simple fabrication of adjustable mirrors by using an initially flat, uniform thickness disk.